Fibers and resins are normally introduced together into a compounding extruder in a solid state. Upon first being converted from a solid to a liquid by a combination of motion, heat, friction, and pressure, thermoplastic resins have a relatively high viscosity, which contributes to fiber breakage as the resins are intermixed with the fibers in the extruder. Some compounding extruders introduce room-temperature fibers downstream of the thermoplastic resin input point in the compounding sequence. Doing so has the disadvantage that relatively cold fibers draw heat out of the melted resin, thereby raising the viscosity of the resin melt stream. The resulting, somewhat more viscous melt stream contributes to fiber breakage during the extruding process.
The foregoing problems and difficulties associated with prior art compression molding techniques would be eliminated if a molder could compound the thermoplastic molding product in-line with the preform-making equipment. Accordingly, the present invention is directed to an apparatus and method for compounding fibers with thermoplastic resins in an extrusion process where the fibers measure one and one quarter inches in length or greater.